The present invention relates to an optical encoder device, and more specifically to the detailed design of an optical encoder device.
An encoder is a device that provides feedback to a closed loop system. The encoder enables a signal interpretation such as to obtain information on a position, velocity, acceleration and/or the like when the encoder works in conjunction with a codewheel or a codestrip. Codewheels are generally used for detecting the rotational motion, for example of a paper feeder drum in a printer or a copying machine, while codestrips are used for detecting the linear motion, for example of a print head of a printer.
Usually, the motion of the codewheel or the codestrip is detected optically by means of an optical emitter and an optical detector. Therefore, the encoder is usually an optical encoder. The optical emitter emits light in a light emission direction towards the codewheel/codestrip. The codewheel/codestrip comprises a regular pattern of slots and bars. According to the position of the slots and bars relative to the light emission direction, the codewheel/codestrip alternately permits and prevents light passing therethrough. The optical detector is positioned behind the codewheel/codestrip, when seen in the direction of the light emission from the optical emitter, and detects a light signal based on the light emitted by the optical emitter and transmitted through the codewheel/codestrip. The detected light signal is either quadruple or sinusoidal and the frequency of said light signal yields an unambiguous information on the motion of the codewheel/codestrip.
Due to the special arrangement of the optical emitter and the optical detector of such an optical encoder, the optical encoder housing for accommodating the optical encoder is generally C-shaped. The optical encoder together with the C-shaped optical encoder housing form a C-shaped optical encoder device. The codewheel/codestrip is passed through the free area (the recess) of the C-shaped optical encoder device and moves such that the optical encoder can detect the slots and bars formed in the codewheel/codestrip. FIG. 2A and FIG. 2C show cross-sections through and FIG. 2B and FIG. 2D show top views of such a C-shaped optical encoder device 201 together with a codewheel 202 and a codestrip 203, respectively. The codewheel 202 and the codestrip 203 are provided with a regular pattern of slots 204 (and bars between the slots 204) which are arranged such that a motion of the codewheel 202 or the codestrip 203, respectively, is unambiguously detectable. Therefore, the codewheel 202 or the codestrip 203, respectively, is passed through the free area 205 of the generally C-shaped optical encoder device 201 which takes up the codewheel 202 or the codestrip 203, respectively. If the codewheel 202 is rotated around the center axis C in a direction indicated by the arrows 206, or if the codestrip 203 is linearly moved in a direction indicated by the arrows 207, respectively, the slots 204 (and the bars between the slots 204) cause an alternating light signal in the optical detector of the optical encoder which results in an unambiguous information on the motion of the codewheel 202 or the codestrip 203, respectively.
Generally, the C-shaped optical encoder device 201 is mounted on a printed circuit board (PCB) which is positioned inside the appliance, e.g. a printer or a copying machine, and which is used for an electrical coupling of the optical encoder to the control unit of the appliance. The C-shaped optical encoder device 201 itself comprises as main components an optical emitter 208 and an optical detector 209. The optical emitter 208 may be a light emitting diode, whereas the optical detector 209 is usually an array of photodiodes. The optical emitter 208 and the optical detector 209 are arranged inside the C-shaped optical encoder device 201 such that a straight optical path 211 results for light, which is emitted by the optical emitter 208 and detected by the optical detector 209. Light, which is emitted by the optical emitter 208 and travels along the optical path 211, is first collimated into parallel light by means of an optical lens 210, which is positioned next to the optical emitter 208, then transmitted through the free area 205 and partly through the codewheel 202 or the codestrip 203, respectively, and finally detected by the optical detector 209, which is placed opposite to the optical emitter 208. Due to the opposite arrangement of the optical emitter 209 and the optical detector 209 relative to the codewheel 202 or the codestrip 203, respectively, a special optical through-beam solution for the codewheel 202 or the codestrip 203, respectively, is provided. This optical through-beam solution provides a good performance for detecting the motion of the codewheel 202 or the codestrip 203, respectively.
However, the available optical encoder devices according to the prior art are manufactured with a large number of piece parts in large-scale processes and with extensive production costs.
FIG. 3A shows a cross-section through a first type of optical encoder device 301 according to the prior art. The first optical encoder device 301 comprises an optical emitter 208 and an optical detector 209 which are arranged on a lead frame 302. The lead frame 302 is buried in a housing material 304 and comprises an electrical circuitry (not shown), which is used for electrically contacting the optical emitter 208 and the optical detector 209. Generally, the optical emitter 208 and the optical detector 209 are each covered with a capsule 303. During manufacturing the optical encoder device 301 the optical emitter 208 and the optical detector 209 are first placed on a single common flat lead frame 302 and then covered with the capsules 303. Afterwards, the flat common lead frame 302 with the optical emitter 208, the optical detector 209 and the capsules 303 is covered with an optical transparent housing material 304. Further, an optical lens 210 is provided directly above the optical emitter 208 and partly inside the housing material 304. Additionally, a window 305 is provided directly above the optical detector 209 and partly inside the housing material 304.
The optical lens 210 and the window 305 are provided to enable a satisfying optical transmission for light through the surface of the housing material 304 at predetermined places. Further, the optical lens 210 is provided to collimate light, which is emitted by the optical emitter 208, into parallel light beams. After manufacturing the optical lens 210 and the window 305 the intermediate device is divided in an optical emitter element 306 and an optical detector element 307. Then, the optical emitter element 306 is placed above the optical detector element 307, as indicated with arrow 308 in FIG. 3A, such that the optical emitter 208 together with the optical lens 210 is placed opposite to the optical detector 209 and the window 305 for forming a C-shaped optical encoder. Finally, the optical emitter element 306 is fixed to the optical detector element 307 with a mounting bracket (not shown). Therefore, light emitted by the optical emitter 208 is collimated by the optical lens 210, transmitted through the free area 205 between the optical emitter 208 and the optical detector 209 and through the window 305 and detected by the optical detector 209. Thus, the first type of optical encoder device 301 represents a folded device comprising the optical emitter element 306 and the optical detector element 307.
FIG. 3B shows a cross-section through a second type of optical encoder device 310 according to the prior art. In contrast to the first type of optical encoder device 301 described above, the second type of optical encoder device 310 is manufactured differently and comprises a C-shaped encoder housing 311 with a free area (recess) 205. The encoder housing 311 comprises optical transparent material and an optical lens 210. An optical emitter element 312 and an optical detector element 313 are separately manufactured and subsequently inserted into respective recesses formed in the encoder housing 311 such that the optical emitter 208 is placed next to the optical lens 210. The optical emitter element 312 and the optical detector element 313 each comprise a lead frame 314, on which the optical emitter 208 and the optical detector 209, respectively, are mounted as well as a housing. The lead frames 314 comprise an electrical circuitry (not shown) for electrically contacting the optical emitter 208 and the optical detector 209, respectively. Therefore, this second type of optical encoder device 310 represents a composed device with individually manufactured elements.
However, the first type of optical encoder device 301 and the second type of optical encoder device 310 according to the prior art have some disadvantages. Among others, they need a large number of piece parts and involve large-scale processing methods and, thereby, cause high production costs.
Therefore, it is an object of the present invention to overcome some or all disadvantages of the prior art.